This project involves the study of protein-protein interactions in two areas. The first is solvent accessibility in folded proteins and in associating proteins. The hydrogen exchange kinetics of peptide amide protons with solvent water is studied in order to determine the extent of solvent accessibility in (a) the folded structure of proteins in solution and (b) the interface of associating proteins. From this, the nature of the protein conformational processes limiting dynamic solvent accessibility in the tertiary structure of folded, globular proteins and in the quaternary structure of associating proteins is analyzed. The system utilized in this project is the association of the STI-trypsin complex. The second area of study is the self association, and the ribosome association, of E. coli ribosomal proteins L7 and L12 and of their analogs in the cytoplasmic ribosomes of N. crassa. BIBLIOGRAPHIC REFERENCES: Lynda M. Ellis, Clare K. Woodward and Victor A. Bloomfield. Hydrogen-Tritium Exchange Kinetics of Soybean Trypsin Inhibitor (Kunitz): Solvent Accessibility in the Folded Conformation. Biochemistry 14, 3413-3419 (1975). Clare K. Woodward and Lynda M. Ellis. Hydrogen Exchange Kinetics Changes Upon Formation of the Soybean Trypsin Inhibitor-Trypsin Complex. Biochemistry 14, 3419-3423 (1975).